Category Archives: Diesel

Ceramic diesel glow plugs – their function and how to install

Glow plug technology can be divided into two major categories – metal sheathed types and  ceramic types. Ceramic glow plugs utilise a heating element which is encased in a special type of ceramic – Silicon Nitride. Ceramic glow plugs have the ability to heat up more quickly than metal types and in addition can gain higher operating temperatures for an extended period of time. They are also more compact making these features especially advantageous in modern engines.

THE MAKE-UP OF A CERAMIC GLOW PLUG

Insulator – The insulator separates the electrically positive (Connection terminal) from the electrically negative part (Metal shell) of the glow plug.

Thread – The thread of a high-quality glow plug is always rolled and never cut. By this production method fast, accurate threads are formed, eliminating the possibility of damage to the glow plug bore in the cylinder head.

Centre electrode – The supply voltage is applied to the coils via the solid centre electrode.

Heating coil – Contrary to a metal glow plug, a ceramic glow plug uses a ceramic heating element.

Ceramic casing – The heating coil or heating element of a ceramic glow plug is encased in a high performance ceramic material: silicon nitride. It protects the coil from the high temperatures and vibrations created by the combustion process. It is also an excellent heat conductor, allowing the heat energy of the coil to be rapidly released into the combustion chamber.

Connection terminal – The supply voltage is applied at the connection terminal. This may be a threaded post to suit a connector which is secured by a nut or an unthreaded post to suit a push-on connector.

Metal shell – The metal shell of a glow plug usually provides the electrically negative pole (ground connection).

Taper seat – The taper seat provides simple but effective gas-tight sealing of the combustion chamber without the need for sealing gaskets, etc. Its compact form also allows bore sizes to be kept to a minimum. The taper faces also provide an excellent electrical ground (earth).

Contacting ring – The contacting ring provides the electrical connection at the junction of the centre electrode and the heating element.

INSTALLATION ADVICE

Particular care must be exercised when installing ceramic glow plugs. When fitted, the ceramic is designed to withstand the arduous events that occur within in the combustion chamber, however they are more susceptible than metal types to damage caused by unsupported side loads or impact. Improper installation can make it unusable or even lead to damage to the engine.

1. Where possible the removal of a glow plug should take place with the engine at operating temperature to assist in releasing the plug.
2. Carefully loosen the glow plug.
3. Remove any loose debris around the glow plug with compressed air.
4. Unscrew the old glow plug.
5. Remove any carbon deposits from the glow plug bore – with a reamer if necessary – then clean and inspect the thread in the cylinder head.
6. Screw the glow plug in by hand until it seats in the cylinder head.
7. Set the torque wrench to the correct tightening torque.
8. Ensure that the socket of the torque wrench is correctly in line with the tightening nut of the glow plug and secure it.
9. Refit the electrical supply connection.

How to avoid diesel fuel leaks

Following feedback from our technical team it’s been identified that fuel leakage from some VAG vehicle diesel filter housings may occur subsequent to fuel filter element replacement.

Due to the position of the fuel filter in the engine compartment, leakage of fuel from the filter housing may subsequently compromise safety and cause engine component damage.

While the integrity of the fuel filter housing is sound, incorrect re-installation of the housing cap may cause misalignment between the filter housing cap and housing sealing surfaces and/or deformation of the sealing O-ring, causing diesel fuel leakage.

The most common cause of filter cap/housing misalignment and subsequent fuel leakage, results from the incorrect tightening of the five fixing screws.

If the correct installation procedure is not followed, then external fuel leakage and engine component damage could result. Often diesel leakage, as described here, leads to suspicions that the fuel filter element is to blame. However, as the fuel filter element is mounted entirely within the filter housing, it cannot cause external fuel leakage if the cap is correctly re-installed.

THE STEPS TO SUCCESS
Replacement of the filter element via the following steps will avoid potential fuel leakage:
1. Remove all screws and the housing cap.
2. Remove the used filter element and sealing O-ring.
3. Remove all diesel/dirt/water residue from the housing using a diesel suction tool.
4. Install a new MANN-FILTER fuel filter element.
5. Wet the new O-ring with diesel fuel and mount it onto the cap.
6. Offer the cap squarely to the housing and push down evenly until sealed centrically.
7. Install and turn all screws down by hand.
8. Tighten all screws in the correct sequence (see diagram, below), to a torque of 5Nm – this is a very important step!

Common Rail Diesels – how to undertake a fuel return flow test

As the diesel engine becomes more efficient, and therefore more popular, with most manufacturers offering them right across their ranges, maintenance and understanding of these systems is obviously becoming more and more important in the automotive industry.

Laser Tools offer a number of diesel technology-based tools and the tool we are focusing on in this article is suitable for common rail diesel engines. Pressure loss on a common rail fuel system can often result in poor or no engine starting, rough running and poor acceleration.

A common reason for pressure loss is excessive fuel being returned to the fuel tank (also referred to as ‘back leakage’). If the injector(s) suffer from excessive back leakage, the fuel pump cannot generate enough pressure to let the system operate correctly. This can be more obvious at start and tickover as fuel pressure (at these low engine speeds) is directly related to engine
revolutions.

A blocked or malfunctioning injector will send more fuel back to the tank, while a worn injector may be injecting too much fuel into the combustion chamber, and thus sending less fuel back to the tank. The 5260 kit makes both conditions obvious. It is comprehensive and (usefully) can cater for up to 10 injectors in one test. 40 adaptors are included for Bosch, Siemens, Denso and Delphi CRD systems.

USING THE TOOL IN 9 EASY STEPS

It’s important to have the engine warmed up, as a coldstart condition can give inaccurate results.

STEP 1: Modern engines are usually fitted with a sounddeadening cover over the top of the engine. Remove this to gain access to the injectors. Then check for obvious faults like leaking fuel pipes, loose or chafed vacuum pipes, or wiring, etc.

STEP 2: The fuel return pipe connectors are secured with wire or metal clips. Remove these and store in a safe place.

PLEASE NOTE: Adaptors are included for Bosch, Siemens, Denso and Delphi CRD systems.


STEP 3: Select the correct adaptor and compare to the vehicle’s return line connector. Fit the adaptors to the flexible tubes from the 5260 chamber block.

STEP 4: On some engines, the fuel return lines share a connection with the fuel pump and fuel can be forced back out from the return lines when the engine is started. So either seal off the ends of the fuel return pipes, or clamp off the main return pipe as illustrated, using Laser Tools’ 4386 hose clamp.

STEP 5: Fit the adaptor and tube to the injectors, keeping them in order. They are a simple push-fit, there is no need to use securing clips.

STEP 6: Hang the chamber block from a convenient point under the bonnet. Keep the tubes tidy, making sure they’re not near any pulleys or belts. Start the engine and leave to idle for a few minutes.

STEP 7: The chambers will start to fill with fuel. Stop the engine when they are 50-75% full. Chambers showing a difference of approximately plus or minus 10% from the others are displaying a fault condition. In this case the no.2 cylinder injector is obviously injecting more fuel into the combustion chamber than the other three.

STEP 8: Any injector which has a back leakage problem will have a higher fuel level in the chamber. When the test is complete, drain the chambers into a suitable container. Place a finger over the chamber vent to avoid spillage as the tube is placed over the container. Lift finger from vent and the fuel will drain into the container.

TO FINISH: Remove the clamp from the return fuel line and refit the return fuel line connectors to the injectors, remembering to fit the securing clips. Before the engine cover is refitted, run the engine for a minute or so and check all lines and pipes for fuel leaks.

How a DPF works and common fault code prompts

Achieving the tough vehicle emissions levels under Euro 5 legislation requires a Diesel Particulate Filter (DPF) to be fitted to collect carbon soot particles generated from the combustion process in a diesel engine.

These particles are microscopic balls of carbon containing pure carbon at their core, which are deposits of different hydrocarbon compounds, metal oxides and sulphur – some of which are potentially hazardous to health.

DPFs, however, are prone to malfunctioning as a result of becoming blocked or full, particularly when the vehicle makes an excessive number of short journeys.

This will result in a fault code appearing (see list of typical DPF fault codes at the bottom of the article), such as ‘P1471 – DPF regeneration not completed’. When this happens, the first response is to try running a regeneration of the filter to see if that solves the problem.

Regeneration variants

Forced regeneration is a simple procedure that can be carried out by a workshop and is usually needed because an active regeneration has not been successful during every day driving by the driver. Depending on the type of diagnostic programme available, this can either be a ‘Static Regeneration’ or a ‘Regeneration Run’.

For this example, we’ll be using the Bosch KTS diagnostic tool as our diagnostic unit of choice.

Static Regeneration procedure

To carry out a Static Regeneration, the vehicle is normally positioned outdoors on a suitable surface and the regeneration is initiated and controlled by the KTS. Strict safety procedures must be observed prior to and during this process.

For a Regeneration Run, the technician must select the programme on the KTS and take the vehicle for a drive at a moderate cruising speed for a suitable period of time – usually about 20 minutes. The KTS initiates the Regeneration Run and monitors the process throughout, so a second person is required to operate the KTS while this is being performed.

Further training

Bosch runs a half day training course (VSD 36) for technicians who wish to effectively diagnose faults with DPFs. The course covers the design and function of a DPF, and what conditions might cause the DPF to block prematurely, giving the technician background information on DPFs before covering the different types of regeneration strategies.

Typical DPF Fault Codes

P1471 – Diesel Particulate Filter (Bank 1) Regeneration not completed

P2002 – Diesel Particulate Filter (Bank 1) Efficiency below threshold

P2003 – Diesel Particulate Filter (Bank 1) Particulate mass too high

P242F – Diesel Particulate Filter (Bank 1) Regeneration not active

P244A – Particulate Filter DIfferential pressure too low

P244B – Particulate Filter Differential pressure too high

P2452 – Particulate Filter Differential pressure sensor malfunction

P2453 – Diesel Particulate Filter Differential pressure sensor malfunction

P2454 – Diesel Particulate Filter Differential pressure sensor voltage too low

P2455 – Diesel Particulate Filter Differential pressure sensor malfunction

P2458 – Particulate Filter regeneration maximum regeneration time exceeded

P2459 – Particulate Filter regeneration, regeneration frequency implausible